Tony Blair is to make his second appearance before the Iraq Inquiry, headed by Sir John Chilcot, on 21 January.
Sixty public seats have been allocated through public ballot, with a third going to bereaved family members.
The Cabinet Secretary Sir Gus O'Donnell is among witnesses called for the first time in the final round of public hearings, starting on Tuesday. Those being recalled include the former foreign secretary Jack Straw and former chief of the defence staff Lord Bryce.
Lindsey German, convener of the Stop The War Coalition, said: "Blair will be met with demonstrations and protests. Military families, former soldiers, peace campaigners, students and trade unionists will all be there."